Pre-treatments for publishing print media

ABSTRACT

A pre-treatment coating composition can include an evaporable liquid vehicle and a pre-treatment coating matrix carried by the evaporable liquid vehicle. The pre-treatment coating matrix in this example can include from 30 wt % to 70 wt % multivalent organic salt including a multivalent metal acetate or a multivalent metal propionate, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder. The low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder in this example can be present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio. Weight percentages in this example are based on dry weight of the pre-treatment coating matrix.

BACKGROUND

Inkjet technology has expanded its application to high-speed, commercial and industrial printing, in addition to home and office usage. This technology is a non-impact printing method in which an electronic signal controls and directs droplets or a stream of ink that can be deposited on a wide variety of substrates. Current inkjet printing technology involves forcing the ink drops through small nozzles by thermal ejection or piezoelectric pressure or oscillation onto the surface of a media. Though inkjet printing is versatile, with certain types of printing and processing applications, there can be challenges related to inkjet or digital printing technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example pre-treatment coating composition in accordance with the present disclosure;

FIG. 2 is a cross-sectional schematic view of the pre-treatment matrix layer applied to a print media substrate and having an ink composition printed thereon in accordance with the present disclosure;

FIG. 3 depicts a flow chart of an example method in accordance with the present disclosure;

FIG. 4 is a graphical representation of an example that illustrates gloss provided by print media having a pre-treatment matrix layer prepared in accordance with the present disclosure applied thereto in accordance with the present disclosure;

FIG. 5 is a graphical representation of a comparative example that provides coefficient of friction (COF) provided by print media having a comparative pre-treatment matrix layer applied thereto relative to pre-treatment matrix layers prepared in accordance with the present disclosure;

FIG. 6 is a graphical representation of a comparative example that illustrates the effect of the ratio of low molecular weight PVA to high molecular weight PVA on dot gain on a pre-treatment matrix layer in accordance with the present disclosure; and

FIG. 7 is a graphical representation of an example that compares mean cyan ink inefficiency provided by print media having comparative pre-treatment matrix layers applied thereto relative to pre-treatment matrix layers prepared in accordance with the present disclosure.

DETAILED DESCRIPTION

A pre-treatment coating composition, and the pre-treatment matrix layer that is formed therefrom (after drying, e.g., solvent evaporation), can be used in the publishing area for providing publishing media suitable for high-speed printing, for example. These coatings can likewise be applied to both sides of the print media substrate to provide a glossy paper appearance both at printed and unprinted areas of the publishing print media. Furthermore, these pre-treatment matrix layers can be prepared so that they essentially match the gloss of the underlying paper media substrate, e.g., glossy substrates may relatively closely retain their gloss and matte paper substrates may relatively closely retain their matte appearance. In addition to providing and/or retaining gloss levels, these pre-treatment coating compositions (applied as pre-treatment matrix layers) can also provide more ink saturation due to enhanced (ink) dot gain compared to other coating layers. Higher dot gain provides greater ink density on a media substrate due to more dot spreading upon printing. This can lead to either enhanced saturation or the same saturation with less ink use compared to other coatings. Furthermore, these pre-treatment matrix layers can also provide durability at an acceptable level for publishing applications, even high speed publishing applications, e.g., from 50 feet per minute (fpm) to 1200 fpm.

In accordance with an example of the present disclosure, a pre-treatment coating composition includes an evaporable liquid vehicle and a pre-treatment coating matrix carried by the evaporable liquid vehicle. The pre-treatment coating matrix in this example includes from 30 wt % to 70 wt % multivalent organic salt including a multivalent metal acetate or a multivalent metal propionate, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder. The low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder in this example are present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio. Weight percentages in this example are based on dry weight of the pre-treatment coating matrix. In further detail, the multivalent salt can include a divalent metal selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof. The dispersed polymeric binder can be, for example, a polyurethane binder, e.g., a polyurethane binder having a weight average molecular weight from 30,000 Mw to 100,000 Mw. In still further detail, the pre-treatment coating composition can include a block copolymer surfactant that stabilizes components of the pre-treatment coating matrix by steric hindrance, and can have a weight average molecular weight from 4,000 Mw to 12,000 Mw with an acid value from 5 mg KOH/g to 30 mg KOH/g.

In another example, a publishing print medium includes a media substrate having a basis weight of 50 gsm to 350 gsm, a first pre-treatment matrix layer on a first side of the media substrate, and a second pre-treatment matrix layer on a second side of the media substrate. The first pre-treatment matrix layer and the second pre-treatment matrix layer in this example independently include from 30 wt % to 70 wt % multivalent organic salt, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder. The low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder in this example are present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio. Weight percentages in this example are based on dry weight of the pre-treatment coating matrix. In one example, the multivalent organic salt includes a divalent metal cation selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof. The pre-treatment coating matrix can include an anion selected from acetate, propionate, or a combination thereof. The dispersed polymeric binder can be a dispersed polyurethane binder, for example. Alternatively or additionally, the dispersed polymeric binder includes a polymer or a copolymer including polyurethane, acrylic, vinyl acetate, polyester, vinylidene chloride, butadiene, styrene-butadiene, acrylonitrile-butadiene, or sulfonated styrene-butadiene.

In another example, a method of preparing a publishing print medium includes coating a first side of media substrate with a first pre-treatment coating composition and a second side of media substrate with a second pre-treatment coating composition, the first and second pre-treatment coating composition in this example including an evaporable liquid vehicle and a pre-treatment coating matrix carried by the evaporable liquid vehicle. The pre-treatment coating matrix includes from 30 wt % to 70 wt % multivalent organic salt, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder. The low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder in this example are present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio. Weight percentages in this example are based on dry weight of the pre-treatment coating matrix. Furthermore, the method includes drying the first pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a first pre-treatment matrix layer, and drying the second pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a second pre-treatment matrix layer. In one more specific example, the media substrate can have a basis weight from 50 gsm to 350 gsm. The first pre-treatment coating composition can be applied to the first side at a basis weight from 0.1 gsm to 10 gsm, and the second pre-treatment coating composition is applied to the second side at a basis weight from 0.1 gsm to 10 gsm. The method can include, for example, printing on both sides of the publishing print medium. Coating the first side and the second side can be carried out in-line with printing, for example. The multivalent organic salt can include a divalent metal cation selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof. Furthermore, the multivalent organic salt can include anion selected from acetate, propionate, or a combination thereof.

When discussing the pre-treatment coating compositions, the print media, and the methods herein, these various discussions can be considered applicable to each of these examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing a dispersed polymeric binder in a pre-treatment coating composition, such a polyurethane can also be used for the publishing print media examples, the method examples, etc., and vice versa.

It is noted that the term “pre-treatment coating composition” refers to the composition used to form a “pre-treatment matrix layer.” Furthermore, to avoid confusion, the pre-treatment coating composition includes an aqueous liquid vehicle, e.g., water or a mixture of water and other volatile liquids that are evaporable therefrom, that carries a “pre-treatment coating matrix,” which is the solids or “dry” formulation carried by the liquid vehicle that when dried on a media substrate, forms a “pre-treatment matrix layer.” Thus, the term “pre-treatment” can be used to describe the pre-treatment coating composition, the pre-treatment coating matrix (the solids present in the coating composition), or the matrix layer (solids that remain as a dried layer on the print media substrate). The solids content of the pre-treatment coating composition (referred to as the “pre-treatment coating matrix”) and the solids content of the pre-treatment matrix layer should be about the same, as both exclude the aqueous liquid vehicle in their calculation. For example, a pre-treatment coating composition includes an evaporable liquid vehicle and a pre-treatment coating matrix (solids of the coating) such that the evaporable liquid vehicle (when evaporated) from the solids, leaves the pre-treatment matrix layer coated on the media substrate. In accordance with this, the evaporable liquid vehicle is not included in weight percent (wt %) calculations for either the coating matrix components or the matrix layer components, e.g., dry weight is provided unless the context dictates otherwise.

In accordance with FIG. 1, a pre-treatment coating composition 100A is shown schematically by example. The structures shown are not to scale, and are merely examples that individually and graphically represent a wider class of structures. As shown, the pre-treatment coating composition includes an aqueous liquid vehicle 110 which includes solids either dispersed or solvated therein. Those solids include, for example, multivalent organic salt 120, low molecular weight polyvinyl alcohol binder 130, high molecular weight polyvinyl alcohol binder 140, and dispersed polymeric binder 150, such as polymers and copolymers including acrylic polymers, vinyl acetate polymers, polyester polymers, vinylidene chloride polymers, butadiene polymers, styrene-butadiene polymers, acrylonitrile-butadiene polymers, polyurethane, acrylic polymers, sulfonated styrene butadiene, or the like.

Regarding the various iterations of the formulations described herein as “pre-treatment” coating composition(s) or matrices, the ingredients that are selected for use can provide a benefit to the pre-treatment coating composition 100A, e.g., formulation stability, etc., and/or can provide a benefit to the pre-treatment matrix layer 100B (not shown in this FIG., but shown in FIG. 2) that is dried and formed on the media substrate using the pre-treatment coating composition. For example, in the pre-treatment coating composition or the pre-treatment matrix layer formed therefrom, the multivalent organic salt 120 acts in part as an ink fixer to contribute to the high image quality by preventing color bleed and other visual artifacts when an aqueous ink is printed thereon. It may also increase image quality by keeping the image close to the surface of the pre-treatment coating. Furthermore, the use of a multivalent organic salt (rather than an inorganic salt, such as chloride, bromide, etc.), and in some examples, multivalent acetates and/or propionates, tends to be less corrosive to some metals, which can be present in various equipment that may come into contact with the pre-treatment coating composition. In further detail, inclusion of the multivalent organic salts described herein can act to stabilize the pre-treatment coating compositions, which in accordance with the present disclosure, can include greater than a 3:1 weight ratio of low molecular weight polyvinyl alcohol binder 130 to high molecular weight polyvinyl alcohol binder 140, and can further include the dispersed polymeric particles 150.

Example multivalent metal salts 120 that can be used include a salt of a multivalent metal and a carboxylate ion such as those present in various organic acids, for example. Examples of multivalent metal cations include divalent metal ions, such as Ca²⁺, Cu²⁺, Ni²⁺, Mg²⁺, Zn²⁺, and/or Ba²⁺; and trivalent metal ions, such as Al³⁺, Fe³⁺, and/or Cr³⁺. In one example, the multivalent metal ion can be Ca²⁺, Mg²⁺ or Zn²⁺. In one aspect, the multivalent metal ion(s) can be Ca²⁺, Mg²⁺, and/or Al³⁺. Examples of organic anions that can be used include carboxylate having the formula RCOO⁻, where R is hydrogen or a low molecular weight hydrocarbon chain, e.g., C1 to C12. When R is H, the organic salt is a multivalent formate, when R is C1 the organic salt is a multivalent acetate, when R is C2, the multivalent salt is a propionate, and so forth. In a more specific example, the multivalent organic salt can include carboxylated anion derived from saturated aliphatic monocarboxylic acid having 1 to 6 carbon atoms (C1 to C6), or in a still more specific example, the carboxylated anion can be derived from a saturated aliphatic monocarboxylic acid having 1 or 2 carbon atoms, e.g., acetate (C1) or propionate (C2). Examples of saturated aliphatic monocarboxylic acid having 1 to 6 carbon atoms may include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, and/or hexanoic acid. In other examples, the carboxy or a carbocyclic monocarboxylic acid has 7 to 11 carbon atoms. In certain more specific examples, the multivalent organic salt can include calcium acetate, calcium propionate, magnesium acetate, magnesium propionate, aluminum acetate, aluminum propionate, zinc acetate, zinc propionate, or a combination thereof.

Regardless of the multivalent organic salt 120 used, whether used singly or as a combination of multivalent organic salts, a total amount of multivalent cationic salt in the pre-coating composition (by dry weight) and in the pre-coating matrix can be from 25 wt % to 75 wt %, from 30 wt % to 70 wt %, or from 35 wt % to 65 wt %, for example. In further detail in examples herein, the multivalent organic salt can be selected that has a solubility (on the basis of anhydrous salt) in water from 15 g multivalent organic salt per 100 mL water (15 g/100 mL solubility) or more, e.g., from 15 g/100 mL to 100 g/100 mL, or from 20 g/100 mL to 75 g/100 mL, or from 25 g/100 mL to 60 g/100 mL). The solubility of the multivalent ion in solution can provide a good mechanism to crash the pigment when an ink composition is applied to the pre-treatment matrix layer, and the multivalence nature of the multivalent metal cation can provide more effective crashing and/or pigment fixation compared to monovalent metal ions.

Thus, with these formulations, images printed on the pre-treatment matrix layer (see 100B of FIG. 2), formed from a pre-treatment coating composition 110A, can be enhanced with respect to both durability and print quality by the presence of the multivalent organic salt 120, as it provides a stable composition including the multiple polyvinyl alcohol binders 130, 140 and a dispersed polymeric binder 150. As one example, this combination provides good image quality, including relatively even image and media gloss and/or enhanced or increased dot gain which can relate to image saturation. These coatings can also provide good rub durability for publishing applications. For example, with respect to image quality, ink compositions printed on the pre-treatment coating matrices of the present disclosure can exhibit enhanced or increased dot gain, meaning the ink dots printed thereon are slightly larger (with more spreading) so that upon digitally printing, a higher ink density can be achieved compared to print media without the coating or even with some other state of the art coatings. Thus, less ink may be used to achieve an acceptable amount of color when printed on the pre-coating matrix, or alternatively, richer color saturation may be achievable with the same amount of ink compared to uncoated media or media coated with some other state of the art coatings.

In further detail regarding the multiple polyvinyl alcohol (PVA) binders, one binder is the low molecular weight polyvinyl alcohol binder 130 and the other binder is the high molecular weight polyvinyl alcohol binder 140. In accordance with examples of the present disclosure, “low molecular weight” polyvinyl alcohol can have a viscosity of a 4 wt % solution from 2.5 mPa·s to 7 mPa·s, from 3 mPa·s to 6 mPa·s, or from 3.5 mPa·s to 4.5 mPa·s. The “high molecular weight” polyvinyl alcohol can have a viscosity from 9 mPa·s to 110 mPa·s, from 10 mPa·s to 60 mPa·s, or from 11.5 mPa·s to 14.5 mPa·s. These molecular weights (e.g., low and high Mw PVA) are thus relative to one another, and can be quantified by viscosity, and in some examples, may further be quantified by weight average molecular weight.

With respect to the use of viscosity to quantify the molecular weight of the polyvinyl alcohols used herein, the viscosities are measured at 20° C. as a 4 wt % polyvinyl alcohol solution in water, as per ISO standard 12058-1:2018(E), which is a dynamic viscosity standard testing protocol. The viscosity value is expressed in millipascal seconds (mPa·s) using a falling ball viscometer. With this methodology, the apparatus includes an inclined measurement tube (falling-ball tube of thermally aged, calibrated, precision borosilicate glass tubing with a coefficient of linear expansion of 3.3×10⁻⁶) filled with liquid to be tested, e.g., polyvinyl alcohol solution (4 wt % in water at 20° C.). One of six balls is selected, depending on the expected viscosity range (No. 1 and No. 2 balls are appropriate, as the viscosity values collected will range from 0.6 mPa·s to 10 mPa·s (Ball No. 1; 15.81 mm diameter) or from 7 mPa·s to 130 mPa·s (Ball No. 2; 15.60 mm diameter). If both balls return results, the value of the slower moving ball will be used. Equipment used for this test can be a Hoepler viscometer (described in DIN 53015:1978), or equivalent. The measurement tube is marked defining distances of 100 mm, and the tube is jacketed to provide temperature control (at 20° C.) and to provide a 10 degree incline. The ends are plugged, with one end including a capillary joined to a hollow space to avoid pressure fluctuations. The polyvinyl alcohol solution is kept completely within the tube and between the plugs. The travel time of the ball between the two marks is used to determine the viscosity of the fluid, based on formulations and calculations published in ISO standard 12058-1:2018(E).

Regarding weight average molecular weight of the polyvinyl alcohol binders, the “low molecular weight” polyvinyl alcohol binder, in some examples, can be further defined, or alternatively defined, to include polyvinyl alcohol binders with a weight average molecular weight from 15,000 Mw to 60,000 Mw, from 15,000 Mw to 50,000 Mw, from 15,000 Mw to 45,000 Mw, from 20,000 Mw to 60,000 Mw, from 20,000 Mw to 50,000 Mw, from 20,000 Mw to 45,000 Mw, or from 25,000 Mw to 50,000 Mw, for example. The “high molecular weight” polyvinyl alcohol binder can be further defined, or alternatively defined herein, to include polyvinyl alcohol binders with a weight average molecular weight from 50,000 Mw to 300,000 Mw, from 60,000 Mw to 300,000 Mw, from 75,000 Mw to 300,000 Mw, from 100,000 Mw to 300,000 Mw, from 50,000 Mw to 200,000 Mw, from 75,000 Mw to 200,000 Mw, or from 100,000 Mw to 250,000 Mw, for example. Notably, as the range of low molecular weight and high molecular weight ranges may overlap in some instances (though the viscosity ranges defining high and low molecular weight above do not overlap), it is noted that these two terms are likewise intended to be relative to one another (low molecular weight is considered to be determined relative to high molecular weight polyvinyl alcohol). Thus, in practice, the ranges for the low and high molecular weight polyvinyl alcohol are not intended to overlap in most instances. Thus, in some examples, irrespective of overlapping overall weight ranges, the low molecular weight polyvinyl alcohol may have a weight average molecular weight from 10,000 Mw to 285,000 Mw lower than the high molecular weight polyvinyl alcohol binder. In a more detailed example, the difference in molecular weight ranges between the low to high molecular weight polyvinyl alcohol can be from 20,000 Mw to 200,000 Mw, or from 30,000 Mw to 150,000 Mw.

The low molecular weight polyvinyl alcohol binder 130 and the high molecular weight polyvinyl alcohol binder 140 can be present in the pre-coating composition or in the pre-coating matrix at a weight ratio from 3:1 to 15:1, from 4:1 to 15:1, from 5:1 to 15:1, from 3:1 to 10:1, from 4:1 to 10:1, or from 5:1 to 10:1, for example. In one example, the weight ratio of low molecular polyvinyl alcohol to high molecular weight polyvinyl alcohol can be from 6:1 to 8:1.

Examples of polyvinyl alcohol binders 130, 140 that can be used include partially hydrolyzed polyvinyl alcohol, fully hydrolyzed polyvinyl alcohol, or copolymers including polyvinyl alcohol, provided they are water-soluble. When describing polyvinyl alcohol herein, this can refer to either the low molecular weight polyvinyl alcohol or the high molecular weight polyvinyl alcohol, or to both in a common formulation. Furthermore, for definitional purposes, 98% hydrolyzed polyvinyl alcohol (or greater, based on percentage of alcohol groups present relative to total side groups of both alcohol and acetate groups) is considered to be fully hydrolyzed polyvinyl alcohol. Polyvinyl alcohol that is less than 98% hydrolyzed polyvinyl alcohol is considered to be partially hydrolyzed. In one specific example, the polyvinyl alcohol used can be partially hydrolyzed, and in more specific examples, the polyvinyl alcohol can be partially hydrolyzed at from 80% to 94%. In other examples, the polyvinyl alcohol binders that can be used include water-soluble copolymers of polyvinyl alcohol and other polymeric groups copolymerized therewith, e.g., copolymers of polyvinyl alcohol and poly(ethylene oxide), polyvinyl alcohol and polyvinylamine, cationic polyvinyl alcohol, acetoacetylated polyvinyl alcohol, silyl-modified polyvinyl alcohol, etc. In one example, the polyvinyl alcohol (which includes water-soluble copolymers thereof) can be included at a concentration where it is fully solubilized in the pre-treatment coating compositions, for example.

In further detail regarding the dispersed polymeric binder 150 in the pre-treatment coating composition, or the polymeric binder in the pre-treatment coating matrix (or that remains with the pre-treatment matrix layer), these dispersed polymeric binder particulates may enhance durability by binding the ingredients of the matrix to each other and to the underlying media. In some examples, the polymeric binder particles can be included to allow ink components to penetrate the matrix, providing a surface morphology for receiving aqueous inkjet ink. Thus, the combination of the high molecular weight polyvinyl alcohol, the low molecular weight polyvinyl alcohol, and the dispersed polymeric binder can provide good durability. The dispersed polymeric binder can be, for example, polymer or copolymer particles including a polyurethane, acrylic, vinyl acetate, polyester, vinylidene chloride, butadiene, styrene-butadiene, acrylonitrile-butadiene, sulfonated styrene butadiene, etc. The weight average molecular weight of the dispersed polymeric binder can be, for example, from 20,000 Mw to 1,000,000 Mw, from 30,000 Mw to 500,000 Mw, from 30,000 Mw to 250,000 Mw, or from 30,000 Mw to 100,000 Mw, for example.

The particle size of the dispersed polymeric binder can be from 10 nm to 1 μm, from 10 nm to 500 nm, from 50 nm to 250 nm, from 50 nm to 200 nm, or from 60 nm to 160 nm, for example. The particle size distribution of the dispersed polymeric binder is not particularly limited. However, it is also possible to use two or more distribution sizes of dispersed polymeric binder particles with their own mono-dispersed particle size distribution can be used in combination.

As used herein, particle size can refer to a value of the diameter of spherical particles, or in the case of particles that are not spherical, can refer to the equivalent spherical diameter of the volume of that particular particle if reshaped at the same density as a spherical particle. The particle size distribution can be in a Gaussian distribution or a Gaussian-like distribution (or normal or normal-like distribution). Gaussian-like distributions are distribution curves that can appear Gaussian in distribution curve shape, but which can be slightly skewed in one direction or the other (toward the smaller end or toward the larger end of the particle size distribution range). In these or other types of particle distributions, the particle size can be characterized in one way using the 50^(th) percentile of the particle size, sometimes referred to as the “D50” particle size. For example, a D50 value of about 25 μm means that about 50% of the particles (by number) have a particle size greater than about 25 μm and about 50% of the particles have a particle size less than about 25 μm. Whether the particle size distribution is Gaussian, Gaussian-like, or otherwise, the particle size distribution can be expressed in terms of D50 particle size, which may approximate average particle size, but may not be the same. In examples herein, the particle size ranges disclosed herein can be modified to “average particle size,” providing sometimes slightly different size distribution ranges.

In one example, the dispersed polymeric binder 150 can be in the form of polyurethane binder particles. In more specific detail, in addition to the molecular weight ranges cited previously for the dispersed polymeric binder, the polyurethane binder particles may have a weight average molecular weight (Mw) from 30,000 Mw to 100,000 Mw, from 30,000 Mw to 80,000 Mw, from 30,000 Mw to 70,000 Mw, or from 40,000 Mw to 70,000 Mw, for example. In one specific example, the polyurethane binder particles having a weight average molecular weight from 40,000 Mw to 70,000 Mw can be further characterized to have a number average molecular weight (Mn) from 20,000 Mn to 30,000 Mn and/or a polydispersity from 2.1 to 2.5. In some examples, the glass transition temperature (Tg) of the polyurethane binder particles can be from 40° C. to 140° C., from 50° C. to 100° C., or from 60° C. to 90° C., for example. Glass transition temperature (Tg) parameters can be measured by Differential Scanning calorimetry (DSC), for example.

In additional detail, the pre-treatment coating compositions (and pre-treatment coating matrices and layers) prepared in accordance with the present disclosure can be further modified in some examples by the inclusion of a surfactant.

In one specific example, however, it has been found that some surfactants provide better performance with respect to image quality and/or durability. As an example, certain surfactants sold under the trade name Disperbyk®, including Disperbyk® 190 as an example, provided better performance than other comparative surfactants, such as Tego® Wet surfactants. That said, either or both may be used in the formulations of the present disclosure. Some surfactants, such as Disperbyk® 190 and the like, may be beneficial for use due to it being sterically stabilizing for some of the dispersed pre-treatment coating matrix components within the pre-treatment coating composition, e.g., by steric hindrance with its long chain size. These polymers may have a molecular weight from 4,000 Mw to 12,000 Mw (or from 5,500 Mw to 8,500 Mw), for example. In further detail, certain surfactants may likewise have some acid groups that form anionic moieties in the pre-treatment coating compositions (in the presence of the aqueous liquid vehicle or water). Even more specifically, these and other similar surfactants may be beneficial as they include a block copolymer that stabilizes components of the pre-treatment coating matrix by steric hindrance, and may have a weight average molecular weight from 4,000 Mw to 12,000 Mw with an acid value (or acid number) from 5 mg KOH/g to 30 mg KOH/g. This combination may provide additional benefits, even though other surfactants may alternatively or additionally be used.

Non-limiting examples of other suitable surfactants include anionic surfactant, nonionic surfactant, cationic surfactant, and combinations thereof. In one example, the surfactant can be a nonionic surfactant. Several commercially available nonionic surfactants that can be used in the formulation of the pre-treatment coating composition include ethoxylated alcohols such as those from the Tergitol® series (e.g., Tergitol® 15S30, Tergitol® 15S9), manufactured by Dow Chemical; surfactants from the Surfynol® series (e.g. Surfynol® 440 and Surfynol® 465), and Dynol™ series (e.g. Dynol™ 607 and Dynol™ 604) manufactured by Air Products and Chemicals, Inc.; fluorinated surfactants, such as those from the Zonyl® family (e.g., Zonyl® FSO and Zonyl® FSN surfactants), manufactured by E.I. DuPont de Nemours and Company; Alkoxylated surfactant such as Tego® Wet 510 manufactured from Evonik; fluorinated PolyFox® nonionic surfactants (e.g., PF159 nonionic surfactants), manufactured by Omnova; or combinations thereof. Suitable cationic surfactants that may be used in the pre-treatment coating composition include long chain amines and/or their salts, acrylated diamines, polyamines and/or their salts, quaternary ammonium salts, polyoxyethylenated long-chain amines, quaternized polyoxyethylenated long-chain amines, and/or combinations thereof.

The surfactant, if present, can be included in the pre-treatment coating composition at from 0.05 wt % to 1.5 wt %. In one example, the surfactant can be present in an amount ranging from 0.1 wt % to 1 wt %. In one aspect, the surfactant can be present in an amount ranging from 0.2 wt % to 0.6 wt %.

Other additives can be added to the pre-treatment coating composition including cross-linkers, defoamers, plasticizers, fillers, stabilizers, dispersants, biocides, optical brighteners, viscosity modifiers, leveling agents, UV absorbers, anti-ozonants, wax, etc. Such additives can be present in the pre-treatment coating compositions in amounts from 0.01 wt % to 20 wt %. However, it is noted that in one specific example, the pre-treatment coating composition (and the pre-treatment matrix layer applied to the media substrate) can be devoid of wax. The term “wax” is defined herein to include both natural waxes and synthetic waxes. Example waxes include petroleum wax, vegetable or plant wax, animal wax, modified plant or animal wax, mineral wax, ceresin wax, montan wax, ozocerite wax, peat wax, paraffin wax, microcrystalline wax, polyethylene wax or polypropylene wax, PTFE wax, polytetrafluoroethylene wax, carnauba wax, bee's wax, paraffin wax, polyamide wax, etc. Furthermore, the binders described herein, such as the polyurethane binder particles, are not considered to be a wax consistent with the present disclosure, as the pre-treatment coating compositions are defined herein to include a polyurethane binder in the form of dispersed particles in the composition or as dispersed particles within the matrix applied and dried on the media substrate.

The pre-treatment coating composition can include these, and in some cases other, solids suspended in an aqueous liquid vehicle, which may be simply water, or may be a combination of water and other evaporable solvents or liquids. That stated, in one example, the aqueous liquid vehicle can be water (or water and any other evaporable liquid component that may be present in the individual components used to formulate the pre-treatment coating composition). Regardless of whether or not there are other evaporable components present or not, the water can be included in the pre-treatment coating composition at from 35 wt % to 90 wt %, from 50 wt %, to 85 wt %, or from 60 wt % to 80 wt %, for example.

Referring more specifically to FIG. 2, a publishing print medium 200A is shown that includes a pre-treatment coating composition (shown at 100A of FIG. 1) that is applied to a media substrate 210 and dried to form pre-treatment matrix layers 100B, which is shown in this example as a layer on both sides of the media substrate where the aqueous liquid vehicle has been evaporated or dried therefrom. It is understood that not 100 wt % of water and/or evaporable solvent is typically removed during drying, as coating layers applied to media tend to retain some moisture, but for purposes of the present disclosure, the pre-treatment matrix layer is considered to be a “dried” coating in a manner suitable for receiving an ink composition when printed thereon.

The media substrate 210 that can be coated with the pre-treatment coating composition and resulting pre-treatment matrix layer 100B can be any substrate that is suitable for receiving the pre-treatment coating composition and which is suitable for use with publishing. The pre-treatment coating composition can include a weight ratio of aqueous liquid vehicle from 1:3 to 10:1, from 1:2 to 9:1, or from 1:1 to 9:1, for example. The aqueous liquid vehicle may be water or may include water and other volatile liquids that evaporate from the media substrate after applying as a coating thereon, e.g., mostly such as less than 10 wt % or less than 7 wt % or less than 5 wt % of the weight of the pre-treatment coating matrix, which is applied as part of the pre-treatment matrix layer on the media substrate after drying. Methods that can be used to apply the coating compositions generally include flexo coating, roll coating, slot-die coating, rod coating such as Mayer rod coating, blade coating, gravure coating, knife-over-roll coating, cascade coating, curtain coating, and the like. Generally, the pre-treatment coating composition can be applied to leave a pre-treatment matrix layer with a basis weight of 0.1 gsm to 10 gsm. In one example, the basis weight can be from 0.3 gsm to 5 gsm, and in another aspect, from 0.3 gsm to 4 gsm. The printed image can be applied, for example, at from 0.1 gsm to 5 gsm or from 0.1 gsm to 3 gsm, for example.

The publishing print medium 200A can be further modified with a printed image 60 by applying an ink composition on one or both sides, for example, and the ink composition can interact with the pre-treatment matrix layer, and the image can be applied with good durability, saturation, dot gain, image gloss, and/or the like. In one specific example, the media substrate 210, such as an offset coated media substrate, may be coated with the pre-treatment coating composition, which is dried to essentially remove evaporable liquid vehicle (usually including evaporable solvent, water, or both) to leave the pre-treatment matrix layer 100B. The image may then be printed thereon using ink printing technologies, such as digital printing/inkjet printing, and dried. Thus, for definitional purposes, the evaporable aqueous liquid vehicle (or some cases water) is not part of the matrix, as it is removed (or mostly removed within tolerances for printing on the “dried” pre-treatment matrix layer) from the pre-treatment coating composition after application to the media substrate.

In addition to offset media, the pre-treatment coating compositions and matrices of the present disclosure can be suitable for use on many types of other substrates of print media, including but not limited to, paper media, nonporous media, swellable media, microporous media, photobase media, coated media, uncoated media, and other types of media including plastics, vinyl media, fabrics, woven substrate, etc. In certain examples, the substrate can be swellable media or microporous media. As mentioned, offset media can likewise be used.

Returning again to FIG. 2, the printed image 260 can be referred to as printed ink, printed indicia, printed matter, or the like. In this example, the printed image can be applied to portions of the pre-treatment matrix layers 100B, which may be the case where some areas are imaged and other areas remain unprinted with ink or coated with a colorless ink, for example. In one example, the printed image can be a pigment-based printed image, and in other examples, the printed image can be a dye-based printed image. These printed images can be applied by inkjet ink or other digital printing technologies, or may be applied by analog printing technologies, for example.

Inkjet inks generally can include a colorant dispersed or dissolved in an ink vehicle. As used herein, “ink vehicle” refers to the liquid fluid in which a colorant is placed to form an ink. Many different types of ink vehicles are available, and a wide variety of ink vehicles may be used with the systems and methods of the present disclosure (for inks to print on the pre-treatment matrix layer). Such ink vehicles may include a mixture of a variety of different agents, including, surfactants, solvents, co-solvents, anti-kogation agents, buffers, biocides, sequestering agents, viscosity modifiers, surface-active agents, water, etc. Though not part of the ink vehicle per se, in addition to the colorants, the ink vehicle can carry solid additives such as polymers, latexes, UV curable materials, plasticizers, etc.

Generally the colorant discussed herein can include a pigment and/or dye. As used herein, “dye” refers to compounds or molecules that impart color to an ink vehicle. As such, dye includes molecules and compounds that absorb electromagnetic radiation or certain wavelengths thereof. For example, dyes include those that fluoresce and those that absorb certain wavelengths of visible light. Generally, dyes are water soluble. Furthermore, as used herein, “pigment” generally includes pigment colorants, magnetic particles, aluminas, silicas, and/or other ceramics, organo-metallics or other opaque particles. In one example, the colorant can be a pigment.

Typical ink vehicle formulations can include water, and can further include co-solvents present in total at from 0.1 wt % to 40 wt %, depending on the jetting architecture, though amounts outside of this range can also be used. Further, additional non-ionic, cationic, and/or anionic surfactants can be present, ranging from 0.01 wt % to 10 wt %. In addition to the colorant, the balance of the formulation can be purified water with other small amounts of other ingredients. In some examples, the inkjet ink may include latex for added durability.

Consistent with the formulation of this disclosure, various other additives may be employed to enhance the properties of the ink composition for specific applications. Examples of these additives are those added to inhibit the growth of harmful microorganisms. These additives may be biocides, fungicides, and other microbial agents, which are routinely used in ink formulations. Examples of suitable microbial agents include, but are not limited to, NUOSEPT® (Nudex, Inc.), UCARCIDE™ (Union carbide Corp.), VANCIDE® (R.T. Vanderbilt Co.), PROXEL® (ICI America), and combinations thereof.

Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid), may be included to eliminate the deleterious effects of heavy metal impurities, and buffer solutions may be used to control the pH of the ink. From 0 wt % to 2 wt %, for example, can be used. Viscosity modifiers and buffers may also be present, as well as other additives known to those skilled in the art to modify properties of the ink as desired. Such additives can be present at from 0 wt % to 20 wt %.

In another example, as shown in FIG. 3 by way of example, a method 300 of preparing a publishing print medium includes coating 310 a first side of media substrate with a first pre-treatment coating composition and a second side of media substrate with a second pre-treatment coating composition, the first and second pre-treatment coating compositions including an evaporable liquid vehicle and a pre-treatment coating matrix carried by the evaporable liquid vehicle. The pre-treatment coating matrix can include from 30 wt % to 70 wt % multivalent organic salt, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 30,000 Mw to 100,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder. The low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder can be present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio (weight percentages based on dry weight of the pre-treatment coating matrix). The method can further include drying 320 the first pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a first pre-treatment matrix layer, and drying 330 the second pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a second pre-treatment matrix layer. The media substrate in this example can have a basis weight from 50 gsm to 350 gsm, from 60 gsm to 300 gsm, or from 60 gsm to 250 gsm, for example.

It is to be understood that this disclosure is not limited to the particular process steps and materials disclosed herein because such process steps and materials may vary somewhat. It is also to be understood that the terminology used herein is used for the purpose of describing particular examples only. The terms are not intended to be limiting because the scope of the present disclosure is intended to be limited only by the appended claims and equivalents thereof.

It is be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

The term “acid value” or “acid number” refers to the mass of potassium hydroxide (KOH) in milligrams that can be used to neutralize one gram of substance (mg KOH/g), such as the polyurethane binders disclosed herein. This value can be determined, in one example, by dissolving or dispersing a known quantity of a material in organic solvent and then titrating with a solution of potassium hydroxide (KOH) of known concentration for measurement.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 to about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. Additionally, a numerical range with a lower end of “0” can include a sub-range using “0.1” as the lower end point.

EXAMPLES

The following examples illustrate the pre-treatment coating compositions and matrices, and data associated therewith. However, it is to be understood that the following are only exemplary or illustrative of the application of the principles of the present compositions print media, and methods. Numerous modifications and alternative pre-treatment coating compositions or matrices may be devised without departing from the spirit and scope of the present compositions, media sheets, and methods. The appended claims are intended to cover such modifications and arrangements. Thus, while the above has been described with some particularity, the following provides further example details.

Example 1 Selection of Fixative Salts and Dispersed Polymeric Binder for Pre-Treatment Coating Compositions

The present evaluation was conducted to determine if there were certain fixative multivalent salts and/or dispersed polymeric binders (or combinations thereof) that provided better gloss than others with respect to the gloss commonly present on publishing print media. If the gloss of the pre-treatment coating composition provides a noticeably different gloss at coated locations compared to printed locations or uncoated locations, then the printed publishing media tends to be not as appealing to end users or consumers of the printed media. To conduct this evaluation, several different publishing pre-treatment coating compositions, or primers, were prepared. Notably, four different Dispersed Polymeric Binders and four different Fixative Salts were prepared using water as a solvent carrier leaving 25 wt % solids content, totaling 16 different pre-treatment coating compositions as set forth in Table 1 below:

TABLE 1 Pre-treatment Coating Compositions Dry Parts by Ingredient Category Weight (wt %) ¹ Latex Polymer Dispersed Polymeric Binder 22.06 ² Salt Multivalent Metal Salt 55.15 Poval ™ 13-88 High Mw PVA (110,000 Mw) in 22.06 in Solution solution with Latex Stabilizer Tego ® Wet 510 Surfactant  0.74 Water Solvent Carrier — ¹ One of four Dispersed Polymeric Binders selected, See Table 2 for specific binder. ² One of four Multivalent Metal Salts selected, See Table 2 for specific salt.

A total of 16 pre-treatment coating compositions that were prepared were hand coated at a 1.5 gsm to 2 gsm dry coating weight basis to Metsaboard Kemi Prime WKL offset coated paper (185 gsm). The coated publishing print media substrates were then dried using a heat gun and printed with colored images using an HP CM8060 Color MFP Edgeline Technology printer with HP A50 inks, which included a total of seven colored inks (CMYKRGB) and unprinted areas remaining white. The unprinted pre-treatment matrix layers and the printed areas on the pre-treatment matrix layers were evaluated for gloss at 75 degrees (no units) using a BYK Gardner 75° Micro-TRI-Glossmeter. The printed areas were evaluated for gloss by averaging all of the printed colors and the unprinted white areas using the following Gloss Scoring metrics: 1=75-90 Gloss; 2=65-75 Gloss; 3=55-65 Gloss; and 4=40-55 Gloss. The data collected is provided in Table 2, as follows:

TABLE 2 Gloss of Unprinted and Printed Pre-treatment Matrix Layers Dispersed Multivalent Metal Salt ID Latex Unprinted Calcium Calcium Calcium Calcium Polymer ID or Printed Chloride Acetate Propionate Nitrate Polyurethane Unprinted 2 1 1 4 Polyurethane Printed 3 2 2 4 Vinyl Acetate Unprinted 2 2 2 2 Vinyl Acetate Printed 3 2 3 3 Acrylic Unprinted 1 1 1 1 Acrylic Printed 3 1 2 3 Sulfonated Unprinted 1 1 1 2 Styrene Butadiene Sulfonated Printed 3 1 2 3 Styrene Butadiene Polyurethane used is available under the trade name PrintRite DP388 from Lubrizol (USA). Vinyl Acetate used is available under the trade name Neocar ® Latex 2300 from Arkema (France). Acrylic available used is under the trade name Raycat ® 78 from Specialty Polymers (USA). Sulfonated Styrene Butadiene used is available under the trade name Novajet ® 3800 from Omnova (Canada).

As can be seen in Table 2, the gloss for both the unprinted sheet portions and the printed portions was better and more uniform with the multivalent organic salts, namely in this example, calcium acetate and the calcium propionate, compared to the multivalent inorganic salts, namely calcium chloride and calcium nitrate.

Example 2 Preparation of Pre-Treatment Coating Compositions for Comparison

Three different pre-treatment coating compositions were prepared for comparison purposes, namely an example pre-treatment coating composition (P-1) prepared in accordance with the present disclosure, a first comparative pre-treatment coating composition that is similar to a commercially available pre-treatment coating composition (P-Comp), and a second comparative pre-treatment composition (P-Comp2) that includes a polyamide wax. The coating compositions were prepared with water as the solvent carrier with a total of about 25 wt % solids content. The formulations prepared are shown in Table 3, as follows:

TABLE 3 Pre-treatment Coating Compositions for Comparison Coating ID P-1 P-Comp P-Comp2 Ingredient Category (dry wt %) (dry wt %) (dry wt %) PrintRite ® DP-388 Polyurethane 23 — 15.5 Latex Polymer Raycat ® 78 Acrylic Latex — 40.9 — Polymer Neocar ® 2300 Vinyl Acetate — 6 — Latex Polymer Poval ™ 4-88 Low Mw PVA 15.4 8 10.4 (31,000 Mw) Poval ™ 13-88 High Mw PVA 1.9 4 15.5 (110,000 Mw) Orgasol ® 2002 Polyamide-12 — — 15.5 EXD Nat 1 Wax Wax Ultralube ® D806 Polyethylene — 6 — Wax Gasil ® 23F Silica Matting — 3 — Agent Tego ® Wet 510 Surfactant — 0.3 0.78 Disperbyk ® 190 Surfactant 0.77 — — BYK ® 018 Defoamer 1.15 2.7 3.2 Calcium Chloride Multivalent — 29 38.8 Inorganic Salt Calcium Acetate Multivalent 57.6 — — Organic Salt Acticide ® M20 Biocide 0.05 0.04 0.05 Acticide ® B20 Biocide 0.14 0.11 0.16 PrintRite ® DP-388 is available from available from Lubrizol (USA). Raycat ® 78 is available from Specialty Polymers (USA). Neocar ® 2300 is available from Arkema (France). Poval ™ 4-88 and 13-88 are both available from Kuraray (USA). Orgasol ® 2002 is available from Arkema (France). Ultralube ® D806 is available from Keim Additec (Germany). Gasil ® 23F is available from PQ Corporation (USA). Tego ® Wet 510 is available from Evonik Industries AG (Germany). Disperbyk ® 190 and BYK ® 018 are available from BYK-Chemie GmbH (Germany). Acticide ® M20 and B20 are available from Thor (USA).

Example 3 Gloss, Coefficient of Friction, and Color Gamut Evaluation

Two of the pre-treatment coating compositions from Table 3 (P-1 and P-Comp) were prepared and hand coated on matte offset coated paper (rolled 45# Verso New Era Matte) at a speed of 300 feet per minute (fpm), as well as on glossy offset coated paper (rolled 60# Verso Sterling Ultra Gloss) at a speed of 200 fpm. The application of the pre-treatment composition (or priming) occurred on both sides of the paper substrates from an anilox roll, transferring the primer first onto a rubber roller and then onto the paper. The applied coat weight ranged from about 0.33-0.36 gsm dry per side. The primer was applied in-line with duplex printing using a T240 HP Pagewide Web Press equipped with HP A50 inks.

A gloss comparison is shown in FIG. 4, which graphically shows the relative gloss levels for unprinted and printed portions using both P-1 and P-Comp pre-treatment coating compositions on both matte and glossy offset coated paper substrates. On the 60# Sterling Ultra Gloss paper, the pre-treatment matrix layer coated using the P-1 pre-treatment coating composition maintained nearly the same level of gloss as the uncoated or unprimed media substrate, whereas the pre-treatment matrix layer formed from the P-Comp pretreatment coating composition lost a significant amount of gloss, leading to a noticeably distracting gloss difference. The same was true for the printed images, though the difference was less significant than in the unprinted areas. Regarding the 45# matte offset paper substrate, the gloss values in both instances were kept about the same, though P-1 exhibited just a small increase in gloss at both the unprinted and printed areas. Thus, though the pre-treatment coating compositions (e.g., the pre-treatment matrix layers formed therefrom) can provide acceptable gloss on glossy paper substrates, as shown by the matte paper substrate example, they can likewise retain the level of gloss of the underlying paper substrate, thus also providing a good pre-treatment coating option for matte media substrates.

An analysis of coefficient of friction (COF) for paper substrates coated with the P-1 and P-Comp pre-treatment coating compositions was carried out to evaluate the amount of paper slip provided by both resulting pre-treatment matrix layers. The data collected is shown in FIG. 5. COF is an attribute considered for printing paper, particularly in high-speed finishing operations, such as during web turns, folding, cutting, stacking etc. COF, and particularly kinetic COF should be high enough so that the publishing print media does not slip during printing and/for finishing. FIG. 5 shows the results of the COF evaluation for various print media which are uncoated (by the pre-treatment coating compositions, but are still offset coated), inkjet printed, coated with the P-1 pre-treatment coating composition, and coated with the P-Comp pre-treatment coating composition. In the case of both the glossy and matte paper substrates, the P-1 pre-treatment coating composition (and resultant pre-treatment matrix layer) showed higher kinetic COF than the paper coated with the P-Comp coating composition.

Color gamut and black optical density (K-OD) of inkjet images printed using HP A50 inks (CMYKRBG) was compared on both types of paper media substrates (matte and glossy) as well as with both pre-treatment coating compositions (P-1 and P-Comp). The data collected is provided in Table 4, as follows:

TABLE 4 Color Gamut and K-OD Pre-treatment Coating Composition ID 45# New Era 60# Sterling Ultra (Color Gamut or K-OD) Matte (300 fpm) Gloss (200 fpm) P-1 (Color Gamut) 326,000 360,000 P-Comp (Color Gamut) 290,000 328,000 P-1 (K-OD) 1.45 1.56 P-Comp (K-OD) 1.4 1.47

In this evaluation, color gamut was measured using a GretagMacBeth Spectrolino Spectroscan Spectrophotometer based on 816 colors. Black optical density (K-OD) was measured using an X-Rite Spectrodensitometer. As can be seen in Table 4, the color gamut and K-OD that were measured on the various samples and the color gamut for the pre-treatment matrix layer prepared with the P-1 pre-treatment coating composition was about 10% greater, and the K-OD was about 3-6% greater. Thus, better color gamut and/or K-OD can be achieved, or the printer could use less ink with no color penalty using the P-1 pre-treatment coating composition paper coated with the P-1 pre-treatment matrix layer.

Example 4 Effect of Low molecular weight PVA to High molecular weight PVA on Dot Gain

Multiple pre-treatment coating compositions similar to the P-1 pre-treatment coating composition set forth in Table 3 were prepared, except that the ratio of low molecular weight to high molecular weight polyvinyl alcohol binder was varied. Dot gain was evaluated and the data provided in FIG. 6. The cumulative dot area and number of black dots (black ink drops on paper) were measured in an area with a fixed, low ink density, in a region of interest (ROI) under a Keyence VHX-6000 digital microscope using a 150×lens. The ROI was fixed at 4124972 μm² in all cases, and all the large ink dots in this ROI, typically ca. 160, were counted and sized, excluding small satellite drops. In this instance, the T400S Packaging WebPress was operated at a variety of speeds ranging from 400 fpm to 1000 fpm, and the data collected is shown in this FIG. The trend line shows that dot gain can be increased with a greater weight ratio of low molecular weight PVA relative to high molecular weight PVA. At about 3:1 (shown as the vertical dotted line) and greater, e.g., 3:1 to 15:1, 3:1 to 8:1 (as shown), etc., enough improvement can be shown to provide an appreciably enhancement in dot gain relative to lower ratios.

Example 5 Dot Gain and Saturation Evaluation

As both calcium acetate and calcium propionate both outperformed calcium chloride in terms of gloss, as shown in Table 2, the formulation including calcium acetate shown at P-1 of Table 3 was further studied relative to P-Comp and P-Comp2 as formulated in accordance with Table 3. Differences between P-1 and the two comparative pre-treatment compositions included (i) the use of calcium chloride in the comparatives (instead of calcium acetate or calcium propionate), (ii) different weight ratios of the low and high molecular weight polyvinyl alcohols (e.g., P-1 had a low Mw PVA to high Mw PVA weight ratio of about 8:1, whereas P-Comp had a low Mw PVA to high Mw PVA weight ratio of about 2:1 and P-Comp2 had a low Mw PVA to high Mw PVA weight ratio of about 2:3), and (iii) surfactant choice was different for the comparative examples (e.g., Disperbyk® 190 was used in P-1 pre-treatment coating composition and Tego® Wet 510 was used in the P-Comp and P-Comp2 comparative examples). It has been found that Disperbyk® 190 tends to provide better results than Tego® Wet 510, so P-1 was prepared by Disperbyk® 190. P-Comp2, on the other hand, included a polyamide wax additive for further comparison to compare against no wax (of P-1) and polyethylene wax (of P-Comp). Though wax can be used in pre-treatment coating compositions of the present disclosure as well, with removal of wax (e.g., polyethylene, polyamide, etc.) along with the presence of the dispersed polymer or latex, the ratio of polyvinyl alcohol (low to high Mw), and the multivalent organic salt can provide good dot gain and durability. Thus, wax may or may not be present to provide good durability, for example, with the formulations of the present disclosure.

Dot gain or drop area refers to the area of ink that is colored upon application of an ink composition to a media substrate. If an ink tends to spread, then there can be more ink coverage, leading to richer colors or the ability to apply less ink to get acceptable ink coverage. Dot gain can be evaluated using imagery from a digital microscope, such as a Keyence VHX-6000 digital microscope using a 150×lens. Measurements can be based on the cumulative dot area and number of dots (ink drops on paper) within that area, e.g., dots counted and/or measured in an area with a fixed, low ink density, in a region of interest (ROI). However, it was also found that ink saturation can be used as a proxy for determining higher dot gain, as higher dot gain leads to less white space between printed droplets, thus providing higher saturation.

Regarding dot gain using a digital microscope, three sets of images were generated to compare the printing performance on pre-treatment matrix layers generated using pre-treatment coating compositions P-1, P-Comp, and P-Comp2 as set forth in Table 3. The image sets were printed on 45# Verso Liberty Gloss Paper with a T240 HP Pagewide Web Press equipped with HP A50 inks and a printer speed of 250 fpm. The cyan ink was used to evaluate dot gain using a microscope. The first set of images was printed at 4% ink saturation (causing the dots to be relatively far apart), and it was determined that average area of the individual dots was about 30% larger in areas printed on the P-1 coated samples compared to the P-Comp or the P-Comp2 coated samples.

The second set of images was printed at 52% ink saturation (causing the dots to be closer together with some dot overlap), and it was observed that average area of the individual dots was also larger in areas printed on the P-1 coated samples compared to the P-Comp or the P-Comp2 coated samples. Likewise, the third set of images was also printed, but at 100% ink saturation (causing the dots to be significantly overlapping with little white space between dots), and it was also observed that average area of the individual dots was also larger in areas printed on the P-1 coated samples compared to the P-Comp or the P-Comp2 coated samples.

In part because of the dot overlap at 52% ink saturation and the significant dot overlap at 100% ink saturation, rather than calculating dot size for comparison, optical density (OD) can be measured as a proxy for dot gain, as shown by Example in FIG. 7. There, the higher OD is along a saturation curve from 0% to 100%. At any given saturation percentage along the curve, by using the P-1 pre-treatment coating composition data of FIG. 7 (e.g., cyan ink printed on the pre-treatment matrix layer prepared from composition P-1) as the baseline OD for a given saturation % level, the inefficiency of the other two comparative compositions can be calculated and expressed as a “mean cyan ink inefficiency” relative to the P-1 data, such as by using the Formula I, as follows:

$\begin{matrix} {{{Mean}\mspace{14mu}{Cyan}\mspace{14mu}{Ink}\mspace{14mu}{Inefficiency}} = {\frac{\left( {P\; 1\mspace{14mu}{OD}} \right) - \left( {{Comparative}\mspace{14mu}{Sample}\mspace{14mu}{OD}} \right)}{\left( {{Comparative}\mspace{14mu}{Sample}\mspace{14mu}{OD}} \right)}*(100)}} & {{Formula}\mspace{14mu} I} \end{matrix}$

Using Formula I, for cyan samples printed using pre-treatment coating composition P1, the values at any saturation percentage would be 0, since it acts as the baseline. Calculating the average mean cyan ink inefficiency within the mid-tone range identified in FIG. 7, the P-Comp pre-treatment coating composition can be calculated to have a mean cyan ink inefficiency of about 21 and the P-Comp2 mean cyan ink inefficiency can be calculated to be about 18.6. The average mean cyan ink inefficiency was determined using nine points in the cyan mid-tone range for the various sample. In this analysis, the higher the number, the more different (worse) the performance compared to the use of the P-1 pre-treatment coating composition. This data indicates that that P-Comp and P-Comp2 comparatives do not provide as good of dot gain as the P-1 compositions, using saturation relative to optical density (OD) as a proxy for dot gain.

It was also determined that wax can provide some enhancements with respect durability in some instances. That stated, the P-1 pre-treatment coating composition tended to perform the best compared to these comparative examples, even without the use of wax. 

What is claimed is:
 1. A pre-treatment coating composition, comprising: an evaporable liquid vehicle; and a pre-treatment coating matrix carried by the evaporable liquid vehicle, the pre-treatment coating matrix, comprising: from 30 wt % to 70 wt % multivalent organic salt including a multivalent metal acetate or a multivalent metal propionate, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder, wherein the low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder are present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio, and wherein weight percentages are based on dry weight of the pre-treatment coating matrix.
 2. The pre-treatment coating composition of claim 1, wherein the multivalent salt includes a divalent metal selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof.
 3. The pre-treatment coating composition of claim 1, wherein the dispersed polymeric binder includes a dispersed polyurethane binder.
 4. The pre-treatment coating composition of claim 4, wherein the dispersed polyurethane binder has a weight average molecular weight from 30,000 Mw to 100,000 Mw.
 5. The pre-treatment coating composition of claim 1, further comprising a block copolymer surfactant that stabilizes components of the pre-treatment coating matrix by steric hindrance, and having a weight average molecular weight from 4,000 Mw to 12,000 Mw with an acid value from 5 mg KOH/g to 30 mg KOH/g.
 6. A publishing print medium, comprising: a media substrate having a basis weight of 50 gsm to 350 gsm; and a first pre-treatment matrix layer on a first side of the media substrate and a second pre-treatment matrix layer on a second side of the media substrate, the first pre-treatment matrix layer and the second pre-treatment matrix layer independently comprising: from 30 wt % to 70 wt % multivalent organic salt, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder, wherein the low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder are present in the pre-treatment matrix layer at a 3:1 to 15:1 weight ratio, and wherein weight percentages are based on dry weight of the pre-treatment matrix layer.
 7. The publishing print medium of claim 6, wherein the multivalent organic salt includes a divalent metal cation selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof, and an anion selected from acetate, propionate, or a combination thereof.
 8. The publishing print medium of claim 6, wherein the dispersed polymeric binder includes a dispersed polyurethane binder.
 9. The publishing print medium of claim 6, wherein the dispersed polymeric binder includes a polymer or a copolymer including polyurethane, acrylic, vinyl acetate, polyester, vinylidene chloride, butadiene, styrene-butadiene, acrylonitrile-butadiene, or sulfonated styrene-butadiene.
 10. A method of preparing a publishing print medium, comprising: coating a first side of media substrate with a first pre-treatment coating composition and a second side of media substrate with a second pre-treatment coating composition, the first and second pre-treatment coating compositions comprising an evaporable liquid vehicle and a pre-treatment coating matrix carried by the evaporable liquid vehicle, the pre-treatment coating matrix, comprising: from 30 wt % to 70 wt % multivalent organic salt, from 5 wt % to 30 wt % dispersed polymeric binder having a weight average molecular weight from 20,000 Mw to 1,000,000 Mw, from 0.5 wt % to 8 wt % of a high molecular weight polyvinyl alcohol binder, and from 10 wt % to 30 wt % of a low molecular weight polyvinyl alcohol binder, wherein the low molecular weight polyvinyl alcohol binder and the high molecular weight polyvinyl alcohol binder are present in the pre-treatment coating matrix at a 3:1 to 15:1 weight ratio, and wherein weight percentages are based on dry weight of the pre-treatment coating matrix; drying the first pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a first pre-treatment matrix layer; and drying the second pre-treatment coating composition to remove evaporable liquid vehicle therefrom to form a second pre-treatment matrix layer.
 11. The method of claim 10, wherein the media substrate has a basis weight from 50 gsm to 350 gsm.
 12. The method of claim 10, wherein the first pre-treatment coating composition is applied to the first side at a basis weight from 0.1 gsm to 10 gsm, and the second pre-treatment coating composition is applied to the second side at a basis weight from 0.1 gsm to 10 gsm.
 13. The method of claim 10, further comprising printing on both sides of the publishing print medium.
 14. The method of claim 10, wherein coating the first side and the second side is carried out in-line with the printing.
 15. The method of claim 10, wherein the multivalent organic salt includes a divalent metal cation selected from calcium, magnesium, iron, aluminum, zinc, or a combination thereof, and an anion selected from acetate, propionate, or a combination thereof. 